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Patching Cracks in Concrete

The technique for patching cracks will depend on the size of the crack.

Narrow Cracks

Remove any loose debris from the crack and surrounding area with a wire brush and broom.

Narrow cracks can be filled with a masonry crack filler that comes in a cartridge designed to be used in a caulking gun. Or you can fill the cracks with a vinyl concrete patching compound applied and smoothed with a putty knife. Vinyl concrete patching compound does not require the use of a bonding agent.

Wide Cracks

Use a small sledgehammer and chisel to undercut the edges of the crack. Undercutting the crack makes it wider at the base than at the surface, providing a mechanical method of "keying" the patch in place for a more secure and permanent repair.

Clean the area in and around the crack with a wire brush and broom. Wash the area with a stream of water.

Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the cracks. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water or coat the edges of the surface to be repaired with bonding agent.

Smooth the mixture with the trowel.

When the patch has set (see manufacturer's instructions for the patch compound you are using), smooth or brush the surface to match the surrounding area.

Caution

Wear gloves, safety glasses, long sleeves and long pants when drilling, hammering or chiseling concrete.

Step 1

Remove any damaged or crumbling concrete. Use a small sledge hammer and chisel to undercut the edges of the damaged area as illustrated.

Step 2

Clean the area in and around the damage with a wire brush and broom. Then wash the area with a stream of water.

Step 3

Use a piece of wood as a form by securing it against the side of the area you intend to repair. Use bricks or other heavy objects to hold it in place. The top of the form should be flush with the desired height of the edge. The form will give you a guide for smoothing the patch.

Step 4

Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the area to be repaired. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water, or coat the edges of the surface to be repaired with bonding agent.

Step 5

Smooth the mixture with the trowel, using the top of the form as a guide.

Step 6

When the patch has set (see manufacturer's instructions for the patch compound you are using), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.

Step 7

Keep off the patched area until it has had time to cure according to the manufacturer's instructions.

Step 1

Remove any loose or damaged concrete from the area to be repaired.

Step 2

Clean the area with a wire brush and broom. Wash the area with a stream of water.

Step 3

Use two pieces of wood as a form by first securing them to each other to form a corner, then placing them against the corner you intend to repair. Use bricks and wooden braces to hold the form in place. The top of the form should be flush with the desired height of the finished corner. The form will give you a guide for smoothing the patch.

Step 4

Mix vinyl patching compound as directed by the manufacturer and trowel the compound into the area to be repaired. Tamp the mixture to remove air pockets. If you use patching mortar instead of vinyl patching compound, either mix it with bonding agent instead of water, or coat the edges of the surface to be repaired with bonding agent.

Step 5

Smooth the mixture with the trowel, using the top of the form as a guide.

Step 6

When the patch has set (see manufacturer's instructions for the patch compound you are using), remove the form and smooth or brush the surface of the patch as necessary to match the surrounding concrete.

Step 7

Keep off the patched area until it has had time to cure according to the manufacturer's instructions.

Step 1

Using a sledge hammer, break up the damaged area of the concrete into pieces.

Good to Know

For projects that don't require a lot of concrete, look for smaller, 10-pound bags of concrete mix. They're easier to manage than full-size bags and don't leave you with as much leftover material to store.

Step 2

Remove the larger pieces of concrete from the area and distribute the smaller pieces of rubble to create a firm bed on which to pour the new slab.

Step 3

Clean the edges of the remaining slab(s) with a broom.

Step 4

Set up wooden (2 x 4 or 2 x 6) forms along the edges of the area to be repaired. The tops of the forms should be flush with the desired height of the finished slab. The forms will give you a guide for smoothing the new slab area.

Step 5

Mix your concrete according to the manufacturer's instructions.

Step 6

Dampen the area to be repaired.

Step 7

Fill the area between the forms with concrete mix. Begin in one corner and work to the middle. Then, begin in the opposite corner and work to the middle again. Fill until the concrete reaches the tops of the forms.

Step 8

Using a board wider than the repair area, drag the board along the forms to smooth out the surface of the repair area. This is called screeding. Remove any excess concrete that piles up along the front of the board.

Step 9

Tap the sides of the forms to settle the concrete.

Step 10

Smooth the surface of the concrete with a darby. a long wooden trowel, working in large half circles from one side to the other. Stop when water appears on the surface.

Step 11

After the water has evaporated, smooth the surface with a trowel.

Step 12

Allow the concrete to set, then smooth or brush it to match the existing slab or walk. Insert a trowel between the concrete and the form and run it along the inside edge of the form.

Step 13

To accurately match the look of the rest of the slab or walk, you may also need to run an edger along the forms and the new concrete. A hand edger is a special tool that rounds and shapes the edge of a poured concrete surface. A hand jointer or groover is a tool used to create a joint in a concrete surface-like a crack in a sidewalk. Use these tools as necessary to reproduce the look of the slab or walk you are repairing.

Step 14

Keep off the patched area until it has had time to cure according to the manufacturer's instructions. A slow cure is best for concrete. For this reason, the manufacturer may recommend that you mist the fresh concrete with water and cover it with plastic for at least three or four days.

Removing Paint from Concrete

Concrete is porous and absorbs paint pretty well, whether you have a painted porch or a paint spill.

Here are some recommendations:

Pressure wash with a 3000 PSI (or higher) pressure washer with a high velocity nozzle.

Scrub the area with a wire brush or sandpaper (before and/or after) pressure washing.

Apply a chemical paint remover made specifically for concrete.

Keep in mind that you may have to repeat these steps more than once.

Caution

Wear protective equipment and follow product instructions when pressure washing or using chemicals.